National Physical Laboratory India
Delhi, India

The National Physical Laboratory of India, situated in New Delhi, is the measurement standards laboratory of India. It maintains standards of SI units in India and calibrates the national standards of weights and measures. Wikipedia.

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Vilan A.,Weizmann Institute of Science | Aswal D.,National Physical Laboratory India | Cahen D.,Weizmann Institute of Science
Chemical Reviews | Year: 2017

We review charge transport across molecular monolayers, which is central to molecular electronics (MolEl), using large-area junctions (NmJ). We strive to provide a wide conceptual overview of three main subtopics. First, a broad introduction places NmJ in perspective to related fields of research and to single-molecule junctions (1mJ) in addition to a brief historical account. As charge transport presents an ultrasensitive probe for the electronic perfection of interfaces, in the second part ways to form both the monolayer and the contacts are described to construct reliable, defect-free interfaces. The last part is dedicated to understanding and analyses of current-voltage (I-V) traces across molecular junctions. Notwithstanding the original motivation of MolEl, I-V traces are often not very sensitive to molecular details and then provide a poor probe for chemical information. Instead, we focus on how to analyze the net electrical performance of molecular junctions, from a functional device perspective. Finally, we point to creation of a built-in electric field as a key to achieve functionality, including nonlinear current-voltage characteristics that originate in the molecules or their contacts to the electrodes. This review is complemented by a another review that covers metal-molecule-semiconductor junctions and their unique hybrid effects. © 2017 American Chemical Society.

Roy A.K.,National Physical Laboratory India
Journal of molecular recognition : JMR | Year: 2011

Molecularly imprinted polyaniline (PANI) film (∼ 100 nm thick) has been electrochemically fabricated onto indium-tin-oxide (ITO) coated glass plate using ascorbic acid (AA) as template molecule. Fourier transform infra-red spectroscopy, scanning electron microscopy, cyclic voltammetry and differential pulse voltammetry (DPV) studies indicate the presence of AA in PANI matrix, which also acts as a dopant for PANI. Further, the AA selective molecularly imprinted PANI electrode (AA-MI-PANI/ITO) has been developed via over-oxidation of AA doped PANI electrode which leads to the removal of AA moieties from PANI film. The response studies using DPV technique have revealed that this molecularly imprinted AA-MI-PANI/ITO electrode can detect AA in the range of 0.05-0.4 mM with detection limit of 0.018 mM and sensitivity of 1.2 × 10(-5) AmM(-1). Interestingly, this AA-MI-PANI/ITO electrode shows excellent reusability, selectivity and stability. Copyright © 2010 John Wiley & Sons, Ltd.

Gupta V.,National Physical Laboratory India
Applied Physics Letters | Year: 2010

Growth mechanism of carbon nanotubes using arc-discharge are not fully understood up to now. Here, I show that the formation of carbon nanotubes and fullerene in a pure carbon arc in helium atmosphere may involve graphene bubbles. Electron microscopy shows the graphene bubbles formation at the anode surface. The growth of fullerene and nanotubes can occur from these bubbles due to a large pressure difference (103 - 104 bar) at the anode interface and can be understood in terms of Young-Laplace law of surface tension. This model can explain the helium pressure dependence of fullerene and carbon nanotube formation. © 2010 American Institute of Physics.

Patra A.,National Physical Laboratory India | Bendikov M.,Weizmann Institute of Science | Chand S.,National Physical Laboratory India
Accounts of Chemical Research | Year: 2014

ConspectusSince the discovery of high conductivity in iodine-doped polyacetylene, many interesting conducting polymers have been developed. Of these, polythiophenes have been most studied as electronic materials, with poly(3,4-ethylenedioxythiophene) (PEDOT) and the water-soluble PEDOT-PSS being the most successful commercially used conducting polymers.The polyselenophene family together with poly(3,4-ethylenedioxyselenophene) (PEDOS) and its derivatives have been shown to have slightly different properties compared to these of polythiophene and PEDOT because of their different electron donating characters, aromaticities (selenophene vs thiophene), oxidation potentials, electronegativities, and polarizabilities (Se vs S). As a result, the polyselenophenes, especially PEDOS and its derivatives, show a lower band gap and higher-lying highest occupied molecular orbital (HOMO) levels compared with those of thiophene and the PEDOT family.In an organic materials context, the PEDOS family offers some advantages over PEDOT derivatives. This Account draws on computational studies, synthetic methods, electrochemical polymerizations, chemical polymerizations, and the materials properties of PEDOS and its derivatives to demonstrate the importance of these novel materials, which lie at the frontier of conducting polymer research. In particular, we show that (i) PEDOS derivatives have a lower band gap (about 0.2 eV) than the corresponding PEDOT derivatives. Consequently, PEDOS derivatives can absorb the solar spectrum more efficiently compared to PEDOT derivatives and the properties of optoelectronic devices based on neutral and doped PEDOS should be somewhat different from these of PEDOT. (ii) EDOS derivatives have a greater tendency to undergo electrochemical polymerization compared to EDOT derivatives and offer stable and smooth polymer films. (iii) The PEDOS backbone is more rigid than the PEDOT backbone. (iv) PEDOS derivatives are excellent electrochromic materials with high transparency, and have higher contrast ratio and coloration efficiency. (v) The PEDOS/C electrode offers better control over the formation and size of nanoparticles through Se···Pt interactions compared with the PEDOT/C electrode.In addition to this, we summarize the synthesis, electrochemical polymerization, materials properties, and computational studies of fused polyselenophene analogues, namely, poly(cyclopenta[c]selenophene), and a series of low band gap thieno- or selenolo-fused polyselenophenes and selenolo-fused polythiophene. Additionally, we discuss oxidative and solid state polymerization to obtain conducting PEDOS, and its derivatives, and made throughout comparison with S-analogue where applicable. We found that EDOS-based derivatives have a greater tendency toward solid state polymerization and working at a temperature about 20 °C lower than that required for EDOT-based compounds.Our results demonstrate the utility of EDOS unit for generating promising materials PEDOS and its derivatives for electronic devices. Consequently, EDOS structure is the basis for many functionalized polymers and copolymers with tunable optoelectronic and redox properties. These interesting properties, which include high conductivity, lower band gap, rigidity, multicolor electrochromism, and rapid redox switching, allow them to be used in a variety of electronic applications. © 2014 American Chemical Society.

Kumar P.,National Physical Laboratory India | Chand S.,National Physical Laboratory India
Progress in Photovoltaics: Research and Applications | Year: 2012

This article aims to review the recent progress and future aspects of organic solar cells (OSCs). Different device designs proposed for efficient light harvesting and their advancements have been discussed. We have discussed various parameters limiting their efficiency and their possible solutions. Special attention has been paid to understand the device physics and its fundamental facets. Open circuit voltage (V oc) is an important parameter in the determination of their efficiency, but the picture behind the real origin of V oc is not very much clear; therefore, this issue has been discussed in detail. Short lifetime is another important issue; therefore, recent progress in stability and related issues has also been discussed. The progress in roll to roll (R2R) processing and demonstration for large-area OSCs has been paid particular attention. The areas, where further advances will help in the commercial realization of this technology, have also been discussed. Copyright © 2011 John Wiley & Sons, Ltd.

Singh S.,National Physical Laboratory India | Naseema Beegum S.,National Physical Laboratory India
Geophysical Research Letters | Year: 2013

The aerosol direct radiative effects (DRE) in the ultraviolet, shortwave, and longwave range due to an unusual dust storm during 21 March 2012 have been quantified from surface measurements of aerosol optical depth (AOD) and radiation fluxes at Delhi, a western Indo Gangetic Plain station. The intrusion of dust over Delhi caused an increase in daily average AOD at 500 nm from 0.6 to 0.8, with a corresponding decrease in Angstrom exponent from 0.4 to subzero value. The dust severely affected the incoming solar radiation flux in the UV, shortwave, and longwave regions. The DRE at surface in the UV and shortwave regions decreased from -4.6 to -5.9 Wm-2 and from -68 to -86 Wm -2, respectively, while the longwave DRE increased from 27 to 45 Wm-2. ©2013. American Geophysical Union. All Rights Reserved.

Bhagavannarayana G.,National Physical Laboratory India | Kushwaha S.K.,National Physical Laboratory India
Journal of Applied Crystallography | Year: 2010

The enhancement of second-harmonic generation (SHG) efficiency by urea doping in tristhioureazinc(II) sulfate (ZTS) single crystals and its correlation with crystalline perfection have been investigated. ZTS is a potential semiorganic nonlinear optical material. Pure and urea-doped single crystals of ZTS have been successfully grown by the slow evaporation solution technique. The presence of dopant has been confirmed and analysed by Fourier transform infrared spectrometry. The influence of urea doping at different concentrations on crystalline perfection has been thoroughly assessed by high-resolution X-ray diffractometry (HRXRD). HRXRD studies revealed that the ZTS crystals could accommodate urea up to a critical concentration without any deterioration in crystalline perfection. Above this concentration, very low angle structural grain boundaries developed and it seems the excess urea above the critical concentration was segregated along the grain boundaries. At very high doping concentrations, the crystals were found to contain mosaic blocks. The SHG efficiency has been studied using the Kurtz powder technique. The relative SHG efficiency of the crystals was found to increase substantially with the increase in urea concentration. The correlation found between crystalline perfection and SHG efficiency is discussed. © 2010 International Union of Crystallography Printed in Singapore-all rights reserved.

Saini P.,National Physical Laboratory India | Arora M.,National Physical Laboratory India
Journal of Materials Chemistry A | Year: 2013

Conducting polymers are at the forefront of nanomaterial's research but the fundamental mechanisms that govern the formation of functional nanostructures and control their electromagnetic (EM) properties are still unknown. Herein, we report for the first time a detailed correlation between acquired morphology, structural, spectral, electrical and EM properties of the polyaniline (PANI) nanostructures synthesized by a template free route using surfactant dopants as structure directing agents. Aniline has been emulsion polymerized in the presence of different sulfonic acids viz. dodecylbenzenesulfonic acid, camphorsulfonic acid, ligninsulfonic acid & cardanolazophenylsulfonic acid and the formed PANIs have been designated as PDB, PCS, PLS and PCD, respectively. The SEM investigations revealed that the morphology is critically dependent on the nature of the dopant, while FTIR, XRD, EPR and UV-visible studies revealed that doping level follows the order PCD < PLS < PCS < PDB, which agrees with electrical conductivity (2.09 S cm-1 for PDB & 0.73 S cm-1 for PCD) and microwave shielding trends (SE T = -23.58 dB and -55.04 dB for PCD and PDB, respectively). The observed SET trend can be attributed to the highest microwave conductivity, dielectric losses & loss tangent with lowest skin depth value for PDB. Such high attenuation levels (i.e. blocking of >99.999% of incident EM radiation) demonstrate the potential of these materials for making future microwave shields. © 2013 The Royal Society of Chemistry.

Shah J.,National Physical Laboratory India | Kotnala R.K.,National Physical Laboratory India
Journal of Materials Chemistry A | Year: 2013

Pure phase barium titanate (BTO) and Cr doped BTO have been synthesized by a facile single step metal-organic decomposition (MOD) method. Thermal gravimetric analysis (TGA) is performed on the processed sample to analyse the thermal stability of the compound. A tetragonal to distorted cubic phase transformation of BTO by Cr doping has been confirmed by X-ray diffraction and Raman spectroscopy. Cr doping in BTO reduced the ferroelectric transition temperature from 122°C to 108°C. A ferroelectric polarization value of 14.5 μC cm-2 for pure BTO was obtained, which decreased to 3.7 μC cm-2 by 1.5 Cr doping. The diamagnetism of BTO partially transformed into ferromagnetic behaviour by Cr-doping at the expense of a decrease in polarization. The magnetoelectric coefficient has been measured by the dynamic MEB method which was recorded as 13 mV cm-1 Oe-1 for 1.5 Cr:BTO at room temperature. Induced electric polarization has been obtained by applying an external magnetic field due to the local interaction of d electron spins with disordered electric dipoles via oxygen vacancies created by the Cr doping in BaTiO3. Such materials possess immense potential in low energy consumption for miniaturized device applications in the area of spintronics, sensors and transducers and multistage memory. © 2013 The Royal Society of Chemistry.

Srivastava A.K.,National Physical Laboratory India
Journal of Biomedical Nanotechnology | Year: 2011

In this study, some of important findings pertaining to ZnO, TiO 2, WO 3, CuO, CdO and Al 2O 3, on novel growth morphologies and related spectroscopic, optical, electrochemical performance and bio-applicability have been elucidated. In this context, some of the important results of the nanotubes of carbon and boron nitride are also illustrated. The importance of electron microscopy and spectroscopy in the investigation of nanomaterials has been discussed. Copyright © 2011 American Scientific Publishers All rights reserved.

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